The invention relates to marine drives, and more particularly to correction of steering torque.
A marine drive having a lower gearcase and a submerged propeller is subject to steering torque, particularly when the drive is trimmed out or trimmed in. Trimming in or out changes the relative pitch angle of the propeller blades to create an imbalance between the downwardly moving blade on one side and the upwardly moving blade on the other side, which right/left imbalance causes a right or left turn. To counteract this steering torque, it is known in the prior art to provide an adjustable trim tab which can be moved left or right through a given adjustment range. The driver selects a trim tab position according to the engine trim position and steering torque that he desires to balance.
The present invention provides another solution for correcting steering torque. In the present invention, the trim tab, which may or may not be adjustable, is provided with a flair on one side thereof along its upper portion. When the drive is trimmed in, the flair is in the mainstream of the water flow and diverts water flow therearound which produces a force on the other side of the trim tab opposite the flair which counteracts steering torque. When the drive is trimmed out, the anti-ventilation plate shrouds the flair from the mainstream of the water flow. This shrouding effect reduces the reaction force produced by the flair.
In one embodiment, the flair is tapered to have increasing lateral width from the bottom of the flair to the top of the flair, such that the more the drive is trimmed in the more of the flair is unshrouded by the anti-ventilation plate, and the more of the flair is in the mainstream of water flow and the greater the lateral width of the flair around which mainstream water flow is diverted, which in turn provides increasing compensating force counteracting the increasing steering torque as the drive is increasingly trimmed in. This embodiment thus provides variable torque correction.